PUB-2015-IAE

Impurities and Electronic Property Variations of Natural MoS2 Crystal Surfaces

Rafik Addou*†, Stephen McDonnell†, Diego Barrera†‡, Zaibing Guo§, Angelica Azcatl†, Jian Wang†, Hui Zhu†, Christopher L. Hinkle†, Manuel Quevedo-Lopez†, Husam N. Alshareef∥, Luigi Colombo⊥, Julia W. P. Hsu†, and Robert M. Wallace*†, "Impurities and Electronic Property Variations of Natural MoS2 Crystal Surfaces​​"
​ACS Nano, DOI: 10.1021/acsnano.5b03309​
Rafik Addou*†, Stephen McDonnell†, Diego Barrera†‡, Zaibing Guo§, Angelica Azcatl†, Jian Wang†, Hui Zhu†, Christopher L. Hinkle†, Manuel Quevedo-Lopez†, Husam N. Alshareef∥, Luigi Colombo⊥, Julia W. P. Hsu†, and Robert M. Wallace*†
MoS2, Electronic properties
2015
Room temperature X-ray photoelectron spectroscopy (XPS), inductively coupled plasma mass spectrometry (ICPMS), high resolution Rutherford backscattering spectrometry (HR-RBS), Kelvin probe method, and scanning tunneling microscopy (STM) are employed to study the properties of a freshly exfoliated surface of geological MoS2 crystals. Our findings reveal that the semiconductor 2H-MoS2 exhibits both n- and p-type behavior, and the work function as measured by the Kelvin probe is found to vary from 4.4 to 5.3 eV. The presence of impurities in parts-per-million (ppm) and a surface defect density of up to 8% of the total area could explain the variation of the Fermi level position. High resolution RBS data also show a large variation in the MoSx composition (1.8 < x < 2.05) at the surface. Thus, the variation in the conductivity, the work function, and stoichiometry across small areas of MoS2 will have to be controlled during crystal growth in order to provide high quality uniform materials for future device fabrication.